>> sure. >> reporter: -- isn't that by definition incumbent protection. >> not necessarily. even if it's a reap district they still have the republican primary. the incumbent is not necessarily safe. >> reporter: true incumbents still aren't safe, but the threat to them in politically gerrymandered districts full of voters in their own party comes from within, not across the aisle, pulling lawmakers even more to the extreme. chris turner, a democrat. >> there is no scenario in which a republican could win my house district. >> reporter: that could pull you left if you did have a primary opponent. >> sure. there is no question. >> reporter: there are different kinds of gerrymandering, packing, putting like-minded voters together or cracking, separating them to dilute their influential. after the 2010 census texas republicans went the cracking route, spreading the democratic vote in austin across republican districts. this time they packed, republican congressman pete